Icing of surfaces is a critical issue for several sectors as well as for the safety of people [1]-[4]. Traditional de-icing methods, such as mechanical scraping, chemical de-icing, and electrothermal de-icing, have proven effective in reducing the consequences of ice buildup. However, these techniques are often costly and require regular maintenance. This underscores the urgent need for research and development of new de-icing and anti-icing technologies that are not only more effective but also environmentally friendly in order to sustainably address the challenges posed by icing in these industries. Hydrophobic coatings represent a significant advancement in surface protection, offering excellent moisture resistance through high contact angles that reduce wetting [5]. These coatings contribute to corrosion protection, facilitate self-cleaning, and enhance other functional properties. The effectiveness of hydrophobic material protection is determined by the composition and manufacturing methods, which affect surface morphology, adhesion, and durability [5]. Solution immersion, spraying, and dipping are among the methods commonly used for manufacturing hydrophobic coatings. The design of low-wettability surfaces is heavily inspired by biomimicry (Figure 1), using nanometric topography methodologies to achieve Cassie-Baxter wetting states. These surfaces, mimicking the structures of animals and plants, have generated increasing interest and led to the development of smart, functional materials characterized by high hydrophobicity and diverse applications [6]. Studies show that these surfaces offer various properties, such as drag reduction, anti-reflective and anti-fouling characteristics, oil-water separation capabilities, and corrosion protection for metals [7]. Modern scientific research has revealed that surfaces with pronounced superhydrophobic properties are capable of effectively removing water droplets before they freeze at sub-zero temperatures [8][9]. Both hydrophobic and superhydrophobic coatings exhibit high frost resistance, making them promising for use in extreme weather conditions. Interest in passive anti-icing strategies based on superhydrophobic surfaces has significantly dominated research in this area in recent years [10][11]. These materials, characterized by low surface energy and a fine micro-nano structure, play a crucial role in preventing ice formation [12][13]. Their design reduces ice adhesion, which helps slow heat transfer. Thus, the use of superhydrophobic surfaces makes ice formation more difficult, which may have potential applications in various fields, such as aeronautics, construction and transport systems, where icing can pose significant problems.

Modern water-repellent surfaces are inspired by lotus leaves, which are naturally hydrophobic. However, materials derived from this inspiration have not yet achieved the desired performance because, although they repel water, they are not oil-resistant, cannot withstand physical stress, are not self-healing, and remain expensive. Slippery liquid-impregnated porous surface (SLIPS) technology, inspired by Nepenthes pitchers, offers a unique coating for industrial and medical surfaces. It uses a porous material impregnated with a lubricating fluid, creating smooth, water-repellent, and self-cleaning surfaces. These slippery surfaces repel a wide variety of contaminants, such as bacteria, ice, oil, and dust. First introduced in 2011 by Wong et al. [16], SLIPS remains repellent under extreme conditions and possesses good self-healing properties, thus distinguishing it from superhydrophobic surfaces. This method uses surface irregularities to retain a lubricant by capillary action. If the surface energies are appropriate and the roughness well chosen, the lubricant fills the irregularities, forming a continuous liquid film that stabilizes the interface. This allows compressible air pockets to be replaced by a less compressible liquid, providing a smooth surface capable of withstanding pressure, while also facilitating the removal of any immiscible external liquid resting on this lubricant layer. Liquid-impregnated surfaces show promise for applications such as anti-icing, anti-corrosion, and drag reduction [17]. However, challenges remain, including lubricant loss due to evaporation, displacement, fouling, or other mechanisms.

Figure 1.Natural superhydrophobic surfaces: (A) lotus leaf [14] and (B) image of an iridescent blue butterfly [15].

This review examines recent technological advances in the field of superhydrophobic coatings, offering an in-depth analysis of their fundamental principles and mechanisms of action. It also highlights the crucial role of nanomaterials in the integration of these coatings. Furthermore, the review addresses the diverse applications of these coatings in various industries. A focus is also placed on the development of liquid-impregnated slippery surface coatings, which present an innovative alternative to superhydrophobic surfaces for anti-icing applications.

Superhydrophobic surfaces have seen significant progress over the past two decades, driven by strong demand in various industrial sectors. The global market for superhydrophobic coatings, valued at approximately US$19.5 million in 2021, is projected to reach approximately US$120 million by 2030, with a compound annual growth rate (CAGR) of 25.6% between 2022 and 2030 [18]. Artificial superhydrophobic surfaces are created using biomimetic techniques inspired by nature, such as the lotus leaf and butterfly wings. These surfaces, with a static contact angle greater than 150˚ and a contact angle hysteresis of less than 10˚, exhibit exceptional properties (hierarchical micro/nanostructures and surface chemistry) characterized by their ability to effectively repel water [19][20]. This phenomenon, known as the superhydrophobicity effect, results in the formation of almost spherical water droplets when they interact with the surface, minimizing adhesion and greatly facilitating their removal. These unique properties are due to the interaction between low surface energy materials and multi-level surface roughness [21]. This dual-scale structure traps air pockets beneath a liquid, reducing solid-liquid contact and promoting droplet rolling, thus giving the surface hydrophobic and self-cleaning properties. However, artificial superhydrophobic micro/nanostructures are brittle under mechanical stress during practical use [22]. Surface micro/nanostructures and air layers can be permanently damaged, causing irreversible degradation of the surface’s superhydrophobicity, which is a major obstacle to the industrial development of these surfaces [23]. Researchers have investigated methods to enhance the durability of brittle micro-nanostructures, including developing composite micro-nanostructures that protect the surface against mechanical wear [24].

The use of low surface energy materials such as fluorinated compounds or silanes is also essential to achieve superhydrophobicity and decrease adhesion with water molecules [14]. Understanding these characteristics is crucial for creating advanced materials with diverse industrial and environmental applications. Superhydrophobic surfaces find varied applications in several industrial sectors, including aerospace, automotive, construction, energy, textiles, architecture, and medical devices. Their development continues, offering innovative solutions to reduce maintenance efforts while improving the durability and performance of the products and infrastructure involved. Interest in self-sustaining hybrid surfaces based on TiO₂ is growing due to their photocatalytic properties, which are well-suited to harsh environments. Semiconducting metal oxides, such as TiO₂, generate photogenerated electron-hole pairs when exposed to high-energy ultraviolet radiation, giving them excellent photocatalytic properties. However, maintaining the long-term stability of superhydrophobic TiO₂-based coatings is challenging because the organic SH components degrade under UV exposure, destroying their anti-wetting properties. Polymer materials, such as PDMS, are valued for their durability and mechanical properties thanks to their stable cross-linked structure. Their hydrophobicity, chemical inertness, high elasticity, ease of processing, and environmental friendliness make them common choices in many everyday objects. Superhydrophobic composite materials, composed of hydrophobic polypropylene, TiO₂ nanorods, SiO₂ nanoparticles, and PDMS, resist wear while maintaining a self-similar rough structure even after destruction of the surface micro-nanostructure, thus preserving hydrophobicity. Furthermore, superhydrophobic surfaces with self-healing properties increase their durability and longevity. Wang et al. [25] developed a UV-stable superhydrophobic (SH) coating from polydimethylsiloxane (PDMS) and TiO₂ nanoparticles, applied by spraying onto various substrates. Long et al. [26] achieved the modification of polypropylene (PP) to increase its hydrophobicity without losing its structural integrity by creating m-SiO₂/PP composites, using modified silica to obtain a 140˚ water contact angle on a polytetrafluoroethylene (PTFE) substrate. This represents a 44% increase compared to pure PP. Analysis reveals that the m-SiO₂ migrates to the face pressed against the PTFE, due to the substitution of hydrogen atoms by fluorine atoms, forming a protective layer. The self-cleaning properties of the material make it an ideal candidate for dust and oil protection applications.

The use of superhydrophobic surfaces shows promise for reducing ice formation and facilitating de-icing and anti-icing. These surfaces prevent ice nucleation and adhesion, thus improving safety and operational efficiency in cold environments. Wang et al. [27] developed nanocomposite films of polydimethylsiloxane (PDMS) and single-walled carbon nanotubes (SWNTs) with hydrophobic properties due to the low surface energy of PDMS and the conductivity of SWNTs. The films switch between hydrophobic anti-icing and low-voltage electrothermal de-icing. Infrared thermometry showed low droplet contact with the superhydrophobic nanocomposite surface, confirming its properties. Joule effect heat distribution analysis demonstrated the nanocomposite’s ability to heat up for active de-icing, which was confirmed experimentally. Deng et al. [28] presented hydrophobic polydimethylsiloxane (PDMS) aggregates loaded with mesoporous silica (mSiO₂) incorporated into a silicone resin with carbon nanotubes (CNTs) to create a near-infrared-sensitive anti-icing/de-icing coating. This coating offers micrometric roughness and low surface energy due to the PDMS@mSiO₂, while the CNTs add a hierarchical micro-nano structure. The coating exhibits superhydrophobic character with a contact angle of 154.3˚ and a delayed freezing time of 440 s at −20˚C, representing significantly superior performance compared to aluminum plates. Furthermore, it maintains strong adhesion and stable anti-icing properties, promising robustness and durability for anti-icing modifications of rotor blades. Jiang et al. [29] developed a layered coating combining polyvinylidene fluoride (PVDF) and carbon nanotubes (CNTs) for improved anti-icing properties. The coating exhibits a contact angle of 163˚, a frost-delay time of 584 s, and low ice adhesion (13.2 kPa). Its multilayer structure, formed by PVDF and CNT particles, ensures robust performance, even after abrasion and chemical exposure. The melting of the PVDF upon heating creates a continuous network, and the use of CNTs enables efficient photothermal conversion, facilitating de-icing at low temperatures under illumination.

Understanding the physicochemical characteristics of salt-based freezing and adhesion solutions in the context of their application to de-icing processes is a crucial aspect of developing effective and environmentally sound strategies. Yao et al. [30] analyzed the ice-adhesion strength (IAS) of NaCl and NaCH₃COO salts on bituminous surfaces at various concentrations and temperatures. The results showed that a 0.5% saline solution can reduce IAS by 40% - 50% compared to pure water, and the adhesion failure threshold is temperature-dependent. The latent heat of fusion (hf) of NaCl solutions (0.5% to 2.5%) increased successively by 45.3 J/g, 63.1 J/g, 79.9 J/g, 90.0 J/g and 117.6 J/g relative to pure water and the freezing temperature (T_F) of NaCH₃COO and NaCl solutions decreased by 1.3˚C and 1.6˚C, respectively. The reduction in T_F and hf increased the nucleation energy barrier (ΔG*) and the increase in salinity transformed the quasi-liquid layer (QLL) of the droplets into a film, thus reducing the contact area. Luo et al. [31] explored how salinity influences ice adhesion at sub-zero temperatures. In their study, they observed that the adhesion of salt ice decreases with increasing salinity. Brine at temperatures above −21.2˚C acts as a lubricant, significantly reducing this adhesion. At −25˚C, below the eutectic temperature, strong adhesion is noted. Hydrophobicity on smooth surfaces also reduces adhesion, with a hydrophobic silicon wafer exhibiting an adhesion strength of 2.4 ± 1.8 kPa at −10˚C with a saline solution. In contrast, seawater ice exhibits an adhesion of approximately 12 kPa even at −25˚C. These results highlight the importance of considering temperature, salinity, and surface characteristics when designing materials that minimize icing of marine infrastructure.

The aerospace, automotive, and energy industries are experiencing increasing demand for durable surfaces with anti-fog, anti-freeze, and anti-fouling properties due to extreme conditions. Ice buildup and fogging affect flight safety, road traffic, and the efficiency of power generation. Conventional superhydrophobic surfaces using Cassie-type wetting to prevent ice formation have limited durability due to the inevitable transition to the Wenzel state at low temperatures and high humidity. They suffer from limitations due to a stable air layer, including poor stability under pressure and an inability to repel certain liquids [50]. To overcome these challenges, materials inspired by the carnivorous plant Nepenthes, called lubricant-impregnated porous surfaces (SLIPS), have been developed, providing a continuous and stable liquid layer. SLIPS improve anti-icing efficiency and offer an alternative to superhydrophobic surfaces (SHS) as an innovative anti-icing material [51]. SLIPS are slippery surfaces that prevent adhesion, allowing viscous liquids, gels, and emulsions to slide freely. Thanks to their anti-wetting and self-cleaning properties, SLIPS coatings are used in a variety of fields, including consumer goods, agrochemicals, electrical equipment, oil and gas, manufacturing, biomedical devices, pharmaceuticals, energy, and utilities [52]. Composed of solid and liquid materials, SLIPS coatings create a durable, wet, and slippery surface, unlike traditional coatings that dry to form a solid surface (Figure 3). The liquid layer seeps into the textured solid and remains functional throughout the product’s lifespan, allowing for immediate operation after application. Innovation in this area highlights the importance of developing preservation and performance solutions in environments exposed to harsh climatic conditions, where ice management is critical.

Figure 3.Coating technologies: (a) traditional and (b) SLIPS [53].

To create a slippery fluid-impregnated porous surface, a suitable lubricant must be selected that penetrates, spreads, and adheres to surface irregularities, taking into account both surface roughness and lubricant properties [17]. The resulting morphology depends on the properties of the liquid, the lubrication, and the surface. At a zero contact angle, a wetting layer forms, covering the solid surface. The durability of slips is a limiting factor in their practical use across various working environments [54]. Slip deterioration is primarily attributed to two factors: a reduction in the amount of oil present and the smoothing of the nanoporous functional layer [55]. This combination affects the effectiveness of slips in their lubrication function. Slip life can be extended by improving characteristics such as substrate roughness, chemical composition, the physical properties of the lubricant, and ambient conditions [56]. A thorough understanding of lubricant degradation mechanisms is essential for designing durable slips.

Xi et al. [57] presented the fabrication of a micro/nano-integrated, lubricant-impregnated surface with a network of conical microcavities and a porous TiO₂ nanostructure (P-SLIPS). Experimental results indicate that the anti-abrasion properties of P-SLIPS are significantly improved, demonstrating a decrease in ice adhesion after 7 sanding cycles. Icing is not observed on P-SLIPS even after 10 cycles, compared to only 3 cycles for SLIPS surfaces. This improvement is attributed to the micro-cone structure, which protects the coating during icing and polishing operations, thus enhancing the anti-icing durability of P-SLIPS. Zheng et al. [58] designed microstructures on SLIPS substrates using direct laser interference lithography (DLIL), followed by a lubricating oil coating to create DLIL-impregnated SLIPS (DLIL-SLIPS). These structures efficiently retain the oil, allowing self-feeding after multiple icing/de-icing cycles, and thus improving anti-icing performance, durability, and robustness. Tests demonstrate that DLIL-SLIPS exhibit improved ice adhesion with an apparent contact angle of 143˚ and an adhesion force of 7.16 kPa, while reducing the coefficient of friction by 63.3% compared to the substrate. Ge et al. [59] developed a durable SLIPS using a microcone composite micropillar (MCMA) structure created by femtosecond laser writing and a thermosensitive polymer transfer method. The MCMA adjusts its anti-icing properties according to temperature by releasing and absorbing lubricant, and can self-regenerate the lubricant to maintain its properties even after depletion. It offers an optimal static icing delay time of 1033 seconds and a low ice adhesion of 2.51 kPa. Its mechanical and chemical durability is high, maintaining an adhesion of less than 20 kPa after 50 de-icing cycles. Yuan et al. [60] analyzed the self-healing performance of SLIPS via icing-repair and abrasion-repair cycles. A stable lubricating layer is obtained by the infiltration of silicone oil into a silanized porous surface. SLIPS exhibit low ice adhesion, even after icing, and the ice slides off under the influence of gravity. Adhesion does not exceed 100 kPa, and the coating withstands 150 icing/de-icing cycles and 100 abrasion cycles, demonstrating the durability of its anti-icing properties, which makes it promising for applications in durable anti-icing materials for aircraft.

Networked surface structures improve the robustness and durability of SLIPS [61]. Studies have shown that the use of textured surfaces, including interconnected microchannels and cross-linked nanosheets, promotes better retention and efficient liquid storage. This advance in surface design significantly improves their performance by offering both strength and efficiency in liquid handling. Wei etal. [62] prepared a slippery liquid-infused phosphate network-like surface (SLIPNS) whose texture is modulated by the phosphating time. This structure allows for excellent oil storage and retention, extends the freezing time of sessile droplets to 436 seconds—nearly ten times longer than an untreated aluminum foil—and reduces ice adhesion tenfold compared to untreated substrates. SLIPNS is distinguished by its durability, antifouling effectiveness, and potential for long-term de-icing/anti-freezing solutions. Li et al. [63] presented the preparation of a superhydrophobic surface by spraying a sepiolite/ZEF-8 hybrid material with a three-dimensional (3D) fibrous porous network structure layered on a magnesium alloy. The injection of silicone oil generates a self-regenerating SLIPS system, providing a reservoir and channel structure for the lubricant. In addition to its self-regenerating and protective properties, SLIPS demonstrates superior corrosion resistance compared to the superhydrophobic surface, thanks to continuous lubrication that blocks the infiltration of corrosive ions. Finally, the corrosion stability of SLIPS remains excellent after 30 days of immersion in a 3.5% NaCl solution.

Aluminum and its alloys, used in various sectors, face contamination and corrosion problems due to their hydrophilicity. Lv et al. [64] propose a fluorine-free method for creating a lubricated porous surface (SLIPS) by chemically etching aluminum to obtain a honeycomb structure, followed by modification with 1-octadecanethiol and silicone oil. This surface exhibits a 3˚ sliding angle for various liquids, displaying superior corrosion resistance compared to the original aluminum. SLIPS surfaces also demonstrate better anti-icing performance and remarkable durability in extreme tests, thus opening up new applications in the marine industry.

To improve the wetting of a substrate by a lubricant, it is essential to increase the chemical affinity between them [65]. This can be achieved by reducing the surface energy of the substrate using a hydrophobic coating, which stabilizes the lubricant layer. Alternatively, modifying the substrate with functional groups or adding adhesive groups can also promote the stabilization of this layer. Lubricant layer stabilization is traditionally achieved by silanization, a process that removes hydroxyl (−OH) groups from the substrate using silane, resulting in the formation of covalent bonds between the silicon and the substrate via Si-O-M bonds (where M represents the substrate). The incorporation of functionality into silica can be achieved by various methods, depending on the type of functionalization and its properties (Figure 4). Traditional surface modification techniques are based on post-synthetic grafting, using compounds such as organosilanes, silazanes and chlorosilanes, which react with free silanol groups on the surface [66].

He et al. [67] proposed a novel sol-gel process for creating lubricant-impregnated surfaces, avoiding the use of multiple polyelectrolytes and post-treatments previously required. The process is based on the layer-by-layer assembly of nanostructured titanium dioxide onto 316 L stainless steel substrates, using a titanium (IV) butoxide solution in an ethanolic medium. The surfaces are then functionalized with fluorinated silanes and impregnated with a fluorinated lubricant, providing excellent liquid-repellent and antifouling properties. The resulting physicochemical characteristics enhance the antifouling performance of the surfaces. Zhang et al. [68] developed a surface functionalization strategy to make lubricants compatible with the surface by grafting a layer of polydimethylsiloxane (PDMS), thereby stabilizing a silicone oil layer. Jing and Guo [69] prepared lubricant-immobilized sliding surfaces (LISS) by grafting polydimethylsiloxane onto ZnO nanorods, using silicone oil as the lubricant. The silicone oil adheres firmly to the zinc oxide, allowing a sliding angle of less than 3˚. The LISS exhibit high omniphobia at room temperature and excellent sliding with hot liquids. In high-temperature tests, the liquids slide at angles of less than 4˚. Under extreme conditions (shear speeds up to 7000 rpm, 400 hours of immersion, and in the presence of strong acids or bases), the LISS maintains remarkable stability and exhibits corrosion resistance, anti-icing, and anti-fouling properties, promoting its practical applications. Zhang et al. [70] fabricated a novel oil-in-water emulsion-type “armor” structure that allows for the spray deposition of an ultra-slippery coating made of polydimethylsiloxane (PDMS), silicone oil (SO), and waterborne epoxy resin (WEP). This flexible-rigid system, in which the WEP encapsulates the silicone oil and the PDMS gel, maintains 81.2% of its oil film even at 5000 rpm, while preserving its slippery properties. Furthermore, the PDMS gel enhances the adhesion between the WEP layer and the substrate, significantly increasing the coating’s tensile strength to 38 N compared to 12 N for a pure PDMS coating. This solution improves lubricant retention and durability, while also providing superior corrosion resistance and antifouling performance. Xing et al. [71] designed a durable polydimethylsiloxane/silicone oil (PDMS-oil) system exhibiting mechanical strength and self-healing properties. Applied to a magnesium alloy, the PDMS-oil coating is formed by the polymerization of a PDMS layer followed by the diffusion of dimethyl silicone oil. An optimal oil concentration of 50 wt% ensures low shear strength, less than 30 kPa, after 20 freeze-thaw cycles. With a slip angle of approximately 30˚ under normal pressure of 10 kPa, the coating also demonstrates excellent corrosion resistance and self-healing capacity, remaining intact after 20 days in a 3.5 wt% aqueous NaCl solution.

Figure 4.Scheme for obtaining organosilanes by grafting and co-condensation [66].

Superhydrophobic coatings hold great promise for a variety of industrial applications due to their exceptional properties. These coatings are self-cleaning, anti-fog, reduce drag, and offer corrosion resistance, as well as anti-icing characteristics. The development of superhydrophobic surfaces with anti-icing and de-icing properties represents a significant advancement in materials science. By integrating functional nanomaterials and strategically designing surface structures, these surfaces provide effective solutions against icing. This progress contributes to improved safety and efficiency in various industrial sectors, further solidifying their usefulness in applications where water management and icing prevention are critical.

Liquid-impregnated surfaces (SLIPS) offer great potential for antifouling coatings, repelling various liquids and facilitating self-cleaning. Created by impregnating a low-surface-tension liquid, they possess a smooth and homogeneous interface. These surfaces are stable under pressure and self-healing, but their performance depends on the amount of lubricant, which can be depleted through evaporation, drainage, or shearing. Understanding the mechanisms and pathways of lubricant depletion allows us to target the factors contributing to lubricant wear and failure, which is crucial for the development of more durable and efficient SLIPS materials. The surface topography is critically important in lubricant retention. Pore dimensions and surface porosity are key factors influencing the wetting behavior of SLIPS surfaces. Another significant method for optimizing lubricant retention is to increase the affinity between the substrate and the lubricant. This can be achieved by applying surface modifiers or polymers that act as crosslinking agents. Despite significant advances, the commercialization of SLIPS remains a distant goal. One of the main challenges is maintaining lubricant retention in surface protrusions. Among the most promising solutions are the creation of functionalized surfaces to increase the durability of SLIPS. Furthermore, integrating several strategies could offer additional benefits.